A universal serial bus (USB) connection has become a common mechanism for coupling electronic devices to one another. A USB cable has a capability for carrying data and for providing electrical power.
A device that provides power to another device via a USB cable can be referred to as a host device and a device that receives power from another device via a USB cable can be referred to as a peripheral device. For example, a computer might have one or more USB ports to which one or more external devices, such as printers, scanners, mice, joysticks, web cams, modems, speakers, telephones, portable disk drives, and other devices, may be connected via a USB cable. If the computer supplied power to one of the external devices, the computer would be considered a host device and the external device would be considered a peripheral device. In another example, a digital music player might connect to a portable disk drive through a USB cable. If the digital music player provided power to the portable disk drive, the digital music player would be considered a host device and the portable disk drive would be considered a peripheral device. As used herein, the terms ‘host’ and ‘peripheral’ refer only to the provision of power from one device to another and do not imply any other relationship between devices.